The present invention relates to a bundle of wires, that is, a cable, used in a wiring system of a vehicle, electric and electronic apparatus, etc., more particularly relates to a cable formed by arranging a plurality of flat cables into a bundle and process of production of the same.
As the conventional cable, that is, wire harness, used as the electric wiring in an automobile or other vehicle, there is known for example the one disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 58-26114. The wire harness 10 disclosed in this publication is obtained, as shown in FIG. 1, by arranging in a flat plane a plurality of covered electric conductors 10a comprised of conductors 10b exhibiting a circular cross-section covered by an insulating material and connecting the adjoining covered electric conductors 10a to each other.
These plurality of covered electric conductors 10a have female engagement portions 10d exhibiting recessed cross-sections formed so as to extend along a longitudinal direction, and male engagement portions 10e. The male engagement portions exhibiting projecting cross-sections fitting with the female engagement portions 10d at symmetric positions 180 degrees apart on the insulating materials 10c of the covered electric conductors 10a. The electric conductors 10a are connected in a flat plane by fitting the female engagement portions 10d and male engagement portions 10e of adjoining covered electric conductors 10a with each other.
Japanese Unexamined Utility Model Publication (Kokai) No. 58-26114 also discloses a wire harness in which insulating materials 10c of adjoining covered electric conductors 10a are connected to each other by heat bonding without providing the female engagement portions 10d and male engagement portions 10e as described above on the insulating materials 10c of the covered electric conductors 10a. 
Further, as the conventional flat cable, the one shown in FIG. 2 has been known. This flat cable 11 is formed by sandwiching and heat bonding between a pair of insulating sheets 11b and 11b having resinous bonding layers 11a at opposing surfaces a plurality of ribbon-like conductors 11c exhibiting schematically rectangular cross-sections arranged in parallel at constant intervals.
In the production of a wire harness 12 using the above flat cable 11, insulating sheets 11b and 11b having a broader width than those shown in FIG. 2 are used and a larger amount of ribbon-like conductors 11c are sandwiched and heat-fused between these insulating sheets 11b and 11b to produce the wire harness 12 as shown in FIG. 3.
This wire harness 12 is used, in accordance with the design of the wiring, by using a not illustrated cutter or the like to form a plurality of cuts 12c extending along the longitudinal direction over predetermined lengths so as to form a plurality of branch cables 12b each including one or more ribbon-like conductors 11c, attaching a not illustrated bundling connector to a front end having aligned end surfaces and connecting the same to a control portion or the like, and attaching not illustrated connectors to the other ends of the branch cables 12b and connecting them to different parts.
Further, as another wire harness using the flat cable 11, there exists one formed by superimposing a plurality of flat cables 11 as shown in FIG. 2 and partially bundling them by a bundling tape or the like.
In the wire harness 10 disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 58 -26114, the cross-section of the conductor 10b is circular, therefore if conductors 10b having different cross-sections are used for the covered electric conductors 10a in accordance with the magnitude of the current used, the sectional shape of the entire wire harness 10 becomes unbalanced due to the difference of thicknesses of the covered electric conductors 10a and therefore the wiring becomes hard, so therefore usually conductors 10b having the same cross-sections must be used for the covered electric conductors 10a. 
Accordingly, it is difficult to select the sectional areas of the conductors 10b in the covered electric conductors 10a in accordance with the used current, so the degree of freedom of the wiring is lowered.
On the other hand, in the wire harness 12 shown in FIG. 3, by making thicknesses of the ribbon-like conductors 11c constant and making the widths thereof appropriately different, ribbon-like conductors 11c having sectional areas in accordance with the magnitudes of the used electric currents can be assembled. However, in the design of the wiring, the lengths of the branch cables 12b are different in many cases, therefore the cutaway portions 12d which are to be cut away, indicated by hatching in FIG. 3, become large and the result is uneconomicalxe2x80x94resulting in the cost rising by that amount. Further, at the time of wiring, the cuts 12c must be formed by a cutter or the like, so the wiring work is troublesome and the cost becomes higher.
Further, when a plurality of flat cables 11 cut into necessary lengths are partially bundled by a bundling tape or the like to form a wire harness, there are no longer any cutaway parts 12d as mentioned above, but the bundling is troublesome, so the cost becomes higher. Further, when passing the cable through a wiring protection tube or a wiring hole at the time of wiring, the bundling tape of each bundling portion sometimes become obstacles.
The problems described above can be solved by for example arranging a plurality of flat cables 11 as shown in FIG. 2 closely together in parallel and connecting adjoining flat cables 11 to each other by heat bonding them so as to produce a wire harness.
However, in such a flat cable 11, in order to prevent the connection portions from peeling, it is necessary to make the width of an ear portion 11d (refer to FIG. 2) of a side edge larger than the pitch of the plurality of ribbon-like conductors 10 arranged.
Accordingly, in the wire harness formed by connecting flat cables 11 with each other by the heat bonding, as described above, the interval between the ribbon-like conductors 11c located at the two sides of connection portions becomes considerably larger than the intervals between the ribbon-like conductors 11c at other positions, so the width of the wire harness becomes larger by that amount.
With such a wire harness having a large width, a larger wiring space becomes necessary when wiring in a limited space such as a vehicle or a housing of an electronic apparatus. Further, when inserting an end of a wire harness into a connector, an ordinary connector having a standard terminal pitch cannot be attached to the end, so it is necessary to provide a special connector.
On the other hand, if making the interval between the ribbon-like conductors 10c located at the two sides of the connection portion the same as the intervals of the ribbon-like conductors 11c at other positions by superposing the ear portions lid of the adjoining flat cables 11 on each other and then connecting them by heat bonding, a step difference is created at the connection portion and therefore it becomes hard to insert the result into the connector and the bending rigidity of this connection portion becomes high and therefore the wiring becomes difficult.
Further, a wire harness 12 formed by connecting flat cables 11 to each other by the heat bonding has a weak area at the connection portion, a susceptibility of the flat cables 11 to separation during handling, and faster melting of the bonding layer 11 a than the insulating sheet 11b at the time of heat bonding and consequently protrusion of the bonded layer 11a from the connection portion. This protruded bonding layer 11a becomes soft under a relatively high temperature environment and is liable to mess up the wire harness 12 itself or peripheral members around it.
An object of the present invention is to provide a cable using a plurality of flat cables which can be produced at a lower cost without creating much of a discarded portion, which needs almost no cutting and other processing at the time of wiring, and by which the wiring can be carried out simply and at a lower cost.
Another object of the present invention is to provide a cable in which the connection portion of flat cables is higher in strength and has no step difference at the connection portion.
Still another object of the present invention is to provide a cable which is structured to enable the pitch of the ribbon-like conductors to be easily made constant and has a high degree of freedom in the wiring design.
Still another object of the present invention is to provide a process of production of a cable capable of achieving the objects mentioned above smoothly and efficiently.
The cable of the present invention is constituted as follows so as to achieve the above objects.
That is, the cable of the present invention is characterized by being provided with a plurality of flat cables comprising one or a plurality of parallel arranged ribbon-like conductors exhibiting substantially rectangular cross-sections and an insulating covering layer formed flat so as to integrally cover the ribbon-like conductors, the plurality of flat cables being arranged closely in parallel in a flat plane and the side edges of the adjoining flat cables being connected continuously or intermittently over predetermined lengths.
The cable of the above configuration can be configured so that each of the plurality of flat cables has a pair of step portions formed at the two side edges of the above insulating covering layer and so that the plurality of flat cables are connected continuously or intermittently over predetermined lengths in a state with the step portions of the adjoining flat cables complementarily joined.
The cable of the above configuration may be configured so that engagement projections are formed at the pair of step portions and the engagement projections mesh with each other in the state with the adjoining flat cables joined with each other.
The cable of the above configuration may be configured so that the pair of step portions have thicknesses t1 not more than the thickness t of the flat cables and so that both are formed on one surface of the flat cable or one is formed at one surface of the flat cable and the other is formed at the other surface of the flat cable.
The cable of the above configuration may be configured so that the lengths of the plurality of flat cables are set to at least two types of lengths.
The cable of the above configuration may be configured so that at least two of the plurality of flat cables have ends at one side arranged in the same plane.
The cable of the above configuration may be configured so that the insulating covering layer is comprised of a thermoplastic resin and so that the flat cables are connected to each other by heat bonding.
Further, the cable of the present invention is characterized by being provided with a plurality of flat cables comprising one or a plurality of parallel arranged ribbon-like conductors exhibiting substantially rectangular cross-sections and an insulating covering layer formed flat so as to integrally cover the ribbon-like conductors, the plurality of flat cables being alternately folded over each other in a state with edges of one sides of the adjoining flat cables aligned with each other and the edges of the one sides being connected continuously or intermittently over predetermined lengths.
The cable of the above configuration may be configured so that each of the plurality of flat cables has step portions formed at the superposed surfaces and so that the plurality of flat cables are connected by heat bonding continuously or intermittently over predetermined lengths in a state with the step portions back to back.
The cable of the above configuration may be configured so that the step portions have thicknesses t1 not more than the thickness t of the flat cables.
The cable of the above configuration may be configured so that the lengths of the plurality of flat cables are set to at least two types of lengths.
The cable of the above configuration may be configured so that at least two of the plurality of flat cables have ends at one side arranged in the same plane.
The cable of the above configuration may be configured so that the insulating covering layer is comprised of a thermoplastic resin and so that the flat cables are connected to each other by heat bonding.
The process of production of the cable of the present invention is characterized by comprising a feed out step of intermittently feeding out a plurality of flat cables in the same direction, a transport step of transporting the plurality of flat cables fed out by the feed out step in a state arranged closely to each other in parallel in synchronization with the feed in the above feed out step, a heat bonding step of continuously or intermittently heat bonding adjoining side edges of the plurality of flat cables transported by the transport step over predetermined lengths, a take up step of taking up the flat cables heat bonded by the above heat bonding step in synchronization with the transport in the above transport step, and a cutting step of cutting the plurality of flat cables at predetermined timings.
The process of production of the above configuration may be configured so that all of the flat cables other than one flat cable among the plurality of flat cables are fed out by predetermined lengths, then the other flat cables are cut by the above cutting step, the feed out of the cut flat cables is made to stop, the one flat cable is fed out by a predetermined length, then the other flat cables stopped being fed out are again fed out, the one flat cable is further fed out by a predetermined length, then the rear end of the one flat cable is cut at the same plane as the front end of the other flat cables.
The process of production of the above configuration may be configured so that first to fourth flat cables are used as the plurality of flat cables and, in the above feed out step, the first and second flat cables are simultaneously fed out, the third and fourth flat cables are fed out after the first and second flat cables are fed out to predetermined lengths, the second flat cable is cut by the above cutting step and the feed out of the second flat cable is made to stop after the third and fourth flat cables are fed out to predetermined lengths, the fourth flat cable is cut and the feed out of the fourth flat cable is made to stop after the second flat cable is cut, the first and third flat cables are fed out to predetermined lengths, then the first and third flat cables are cut with their rear ends in the same plane.